Solid-state letter display device

ABSTRACT

A plurality of luminous diodes and a driving circuit therefor adapted to cause selected combinations of the luminous diodes to luminesce to display selected letters are formed on the same or different sides of a substrate and the assembly is encapsulated by a transparent molded protective coating. The driving circuit in the form of a diode matrix circuit is fabricated by the integrated circuit technique.

United States Patent Nakamura 54] SOLID-STATE LETTER DISPLAY DEVICE [72]Inventor:

[73] Assignee:

Tadashi Nakamura, Ise-City, Japan lse Electronics Corporation, lse-City,Japan [22] Filed: Julie 5,1969

[211 App]. No.: 830,706

[30] Foreign Application Priority Data July 9, 1968 Japan ..43/476l9 52us. c1 ..315/l69, 313/108 .1105 37/00 Field or Search ..307/303;313/108, 108 1);

1451- 4 Feb. 8, 1972 [56] References Cited UNITED STATES PATENTS2,951,970 9/1960 Matarese ..315/169 3,308,452 3/1967 Michel et al...315/169 x 3,330,983 7/1967 Cusano et a1... ..313/108 3,343,155 9/1967Pahlavan ..3i5/l69 x 3,354,342 11/1967 Ohntrup 8t al ..3l5/169 x PrimaryExaminer-Roy Lake Assistant ExaminerLawrence J Dahl Attorney-Chittick,Pfund, Birch, Samuels & Gauthier [57] ABSTRACT A plurality of luminousdiodes and a driving circuit therefor adapted to cause selectedcombinations of the luminous diodes to lurninesce to display selectedletters are formed on the same or different sides of a substrate and theassembly is encapsulated by a transparent molded protective coating. Thedriving circuit in the form of a diode matrix circuit is fabricated bythe integrated circuit technique.

1 Claims, 4 Drawing Figures SOLID-STATE LETTER DISPLAY DEVICE IBACKGROUND OF THE INVENTION This invention relates to a novelsolid-state letter display device.

Among conventional letter display devices may be mentioned a lightspot-type display device employing discharge tube-type display tubes,fluorescent display tubes or groups of small lamps. These prior devicesare not advantageous in that the physical dimensions of the devices arelarge when compared with those of the letter or characters to bedisplayed or the number of letters to be displayed because all .of thesedevices utilize vacuum tubes, require relatively high voltage andrelatively large power, have poor space factor and require independentdriving circuits.

Recently developed electronic circuits require miniaturization of thedisplay device itself, low operating voltage, small driving power anddecreased thickness of the device because of the tendency of utilizingintegrated circuits and large scale integrated.

SUMMARY OF THE INVENTION It is therefore an object of this invention toprovide a new and improved letter display device which can eliminatedisadvantages of the above described types of conventional displaydevices and can satisfy the requirements of modern display devices.

One of the features of this invention lies in a solid-state letterdisplay device wherein well-known luminous diodes are used as thedisplay elements, the display driving circuit is formed by the techniqueof the integrated circuit so that these elements are formed on asubstrate and are then molded into a unitary structure. Accordingly, thesolid-state letter display device embodying this invention ischaracterized in that it does not utilize any vacuum tube and that it isof small size and thin.

Another feature of this invention lies in a solid-state letter displaydevice wherein luminous diodes and a display driving circuit are formedon a single-semiconductor wafer as an integrated circuit and are thenmolded into a unitary structure.

Still further feature of this invention is to provide a solidstateletter display device capable of displaying a number of letters.

In accordance with this invention there is provided a solidstate letterdisplay device characterized by comprising a substrate, a plurality ofluminous diodes which are formed on the substrate and arranged such thatwhen they are suitably combined they can display any desired letter, adriving circuit for selectively exciting the luminous diodes, saiddriving circuit being formed on the substrate by the integrated circuittechnique and a protective coating encapsulating the substrate, theluminous diodes and the driving circuit. The substrate may be anelectric insulator, a metal plate or a semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages togetherwith organization and operation of this invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a perspective view of a solid'state letter display device orunit embodying the principle of this invention with a portion of thecasing broken away;

FIG. 2 is a partial sectional view showing the relation between asubstrate and luminous elements;

FIG. 3 shows a diagram of one example of a diode matrix driving circuitemployed in this invention and FIG. 4 is a perspective view of asolid-state display device for displaying a plurality of letters.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1illustrating a perspective view, partly broken away, of a novel displayunit for displaying digits, reference numeral indicates an insulatingsubstrate of ceramic and the, like on which are formed a group ofdisplay elements a through h for constituting digits 0 through 9inclusive wherein elements g and g are formed electrically integral.These elements are comprised by luminous diodes having PN- 10 junctions.The luminous diode is a solid-state luminous element typicallyconsisting of GaAs, and as is well known in the art luminesces by theinjection of charge carriers through the PN-junction by the applicationof a voltage and the recombination of such charge carriers. According tothis invention, a preformed group of luminous diodes a through h isbonded to the substrate 10. As shown in FIG; 1, a driving circuit 20formed by the integrated circuit technique is also bonded to thesubstrate. As will be described later in more detail, the

. driving circuit is comprised by a diode matrix circuit adapted toselect predetermined combinations of display elements and to cause themto luminesce to form desired digits. One example of such a diode matrixcircuit is illustrated in FIG. 3.

The diode matrix circuit shown in FIG.'3 is a so-called erasing systemselecting circuit wherein the number of diodes utilized is decreased. InFIG. 3 reference numeral 0 through 9 represent terminals correspondingto respective digits to be displayed and terminals a through hcorrespond to respective luminous diodes shown in FIG. 1. It is nowassumed that after closing a switch S, a wiper W is connected to aterminal corresponding to a digit desired to be displayed, then thedigit will be displayed by a selected combination of luminous diodes.Thus for example, digit 3 is assumed to be displayed. Upon connectingthe wiper W to terminal 3, diode D, will short circuit element f, diodesD and D element e and diodes D and D elements g and g. As a result,voltage is applied to elements a, b, c, d and h alone so that as can bereadily understood from FIG. 1 these elements cooperate to display digitAccording to this invention the diode matrix circuit is fabricated by awell-known integrated circuit technique which may be either multitip,monolithic or mixed integrated circuit. In this manner, the circuitsubstrate 20 comprising an integrated circuit is of extremely smallsize. According to this invention, the circuit substrate 20 is bonded tothe substrate 10 either on the front surface thereof as shown in FIG. 1or on the rear surface. In addition to terminals 0 through 9, thecircuit substrate 20 requires two more terminals for the source andground. Thus there are 12 terminals. In FIG. I these terminals are shownby terminals T. v

As best shown in FIG. 3, it is necessary to connect circuit substrate 20to respective luminous elements a through h. FIG. 2 is a cross-sectionalview to illustrate the manner of deriving out lead wires to respectiveelements when the circuit substrate 20 is bonded to the rear surface ofthe substrate 10. More particularly, luminous elements are bonded to thefront surface of the substrate and two perforations ll and 12 areprovided near the opposite ends of. each luminous element. Groundinglead 30 connected to the lower electrode of the luminous element extendsthrough the perforation 11 while an exciting lead connected to the upperelectrode extends through the perforation 12 to a driving circuit.

A protective coating 40 of a resinous material, for example, is moldedto encapsulate the assembly,- as shown in FIG. 1. In order to makevisible the luminous elements, at least the front portion of theprotective coating 40 should be transparent. Thus, FIG. 1 shows asolid-state letter display device or unit embodying this invention.

As can be noted from the foregoing description, the novel letter displaydevice is characterized by having no vacuum tube or filament. Inaddition, since the luminous elements and mechanical vibrations andshocks. Further, as a driving circuit and luminous diodes are fabricatedby the integrated circuit technique it is possible to operate them withlow voltage and low power. For this reason the novel display device canbe operated directly from an integrated circuit system. If the portionof the protective coating were constructed to act as an optical lens,more easy reading of the displayed letter would be possible. Whensuitably colored the coating acts as a filter. lnasmuch as the luminouselements utilized in this invention are comprised by luminous diodes,where indium and phosphorus are used in the semiconductor material, theluminous elements will emit red colored, while zinc and cerium provideblue colored. In this manner, letters of different colors can bedisplayed.

Although in the above embodiment, a plurality of independent luminouselements and an integrated driving circuit were bonded to a commoninsulating substrate of ceramic or the like, it will be obvious to thoseskilled in the art that such luminous elements and driving circuit maybe formed on a single-semiconductor wafer by the integrated circuittechnique. Where a metal plate is utilized as the substrate to act asone of the electrodes of the luminous diodes, not only the constructionof the assembly can be simplified but also the efficiency of heatdissipation can be improved.

FIG. 4 shows a perspective view of a modified embodiment of thisinvention wherein a plurality of display unitsshown in FIG. 1 arearranged in side by side relationship to simultaneously display a numberof letters or numerals of several orders of magnitude. 7

Although the invention has been shown and described in terms ofpreferred embodiments thereof numerous changes and modifications mayoccur to one skilled in the art within I the scope of this invention asdefined in the appended claim.

What is claimed is:

1. A self-contained solid-state character decoder display devicecomprising:

a thin support substrate having a rectangular area generally the size ofa character space occupied in a display;

a plurality of luminous PN-junction diode display elements supported onsaid substrate in the form of a character raster with power and groundelectrical leads respectively from each side of said PN-junctionprojecting through said substrate; I

a set of plug connection terminals extending from one edge of saidsubstrate, one terminal for each character to be selected and inaddition power and ground terminals;

a unitary diode matrix decoder circuit supported on said substrateoutside the area occupied by said character raster, said circuit having:

a first set of leads connected respectively to said power leads of saiddisplay elements and a second set of character selection leads with adiode connected selection circuit from each character selection lead ofsaid second'set to a predetermined combination of leads of said firstset,

circuit connections from said ground terminal to said ground leads ofall of said display elements, and

circuit connections from said power terminal through respectiveresistors to each lead of said first set; and an encapsulating shell forsaid substrate providing a transparent area over the area occupied bysaid display elements and having said terminals projecting therefrom.

1. A self-contained solid-state character decoder display devicecomprising: a thin support substrate having a rectangular area generallythe size of a character space occupied in a display; a plurality ofluminous PN-junction diode display elements supported on said substratein the form of a character raster with power and ground electrical leadsrespectively from each side of said PN-junction projecting through saidsubstrate; a set of plug connection terminals extending from one edge ofsaid substrate, one terminal for each character to be selected and inaddition power and ground terminals; a unitary diode matrix decodercircuit supported on said substrate outside the area occupied by saidcharacter raster, said circuit having: a first set of leads connectedrespectively to said power leads of said display elements and a secondset of character selection leads with a diode connected selectioncircuit from each character selection lead of said second set to apredetermined combination of leads of said first set, circuitconnections from said ground terminal to said ground leads oF all ofsaid display elements, and circuit connections from said power terminalthrough respective resistors to each lead of said first set; and anencapsulating shell for said substrate providing a transparent area overthe area occupied by said display elements and having said terminalsprojecting therefrom.